potential effects of microclimatic factors in environmental design of building in iraq context

7/27/2019 Potential Effects of Microclimatic Factors in Environmental Design of Building in Iraq Context

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83

International Journal of

Science and Engineering Investigations vol. 2, issue 15, April 2013

ISSN: 2251-8843

Potential Effects of Microclimatic Factors in EnvironmentalDesign of Building in Iraq Context

Ahmed Hasson1, Abdul hussain Al-Askari

2

1Mechanical Engineering Department, College of Engineering, Nahrain University, P.O. Box 64040, Jaderia, Baghdad, Iraq

2Architecture Engineering Department, College of Engineering, Nahrain University, P.O. Box 64040, Jaderia, Baghdad, Iraq

([email protected], [email protected])

Abstract -At the present the building designers and researchersin the region often find it is difficult to identify reliable and

current weather data and information. Although available freemeteorological data are available, not always applied correctlyand well understood by the users, because data complicity andthe abstraction of sustainable design concept.

This study discusses a novel study and develops theimportant climatic data in Iraq for sustainable building design.Base for analysing the long term weather data over the past 50years and examine the practical issues of building design,useful climatic information and patterns are identified.

The provided information will enable people to better understand the trends of local climate and build up theresources for assessing important issues of renewable energy

and environmental design and to determine indoor environmental quality.

The results indicated that the annual average of monthlymean during 50 years recording of global solar radiationincidents increased by 3.3%. While the results of the ambienttemperature analysis show that mean annual temperaturesmeasured Baghdad over the long term at increased by 7%.

During the long-term (50 years) recording period, theannual cooling degree-day value has increased by 16%, whilethe analysis of annual degree-day data over the same periodindicates an even greater reduction of 26%.

The climatic data currently being used for energy design

calculations leads to inaccuracies in predictions of energy use.Heating coefficients were consistently positive and their

values varied between 0.1, in 0.46, while albedo values varied between 0.19 and 0.37. The results indicated that there is littlemonthly variation in the values of nocturnal net radiation.

Keywords- Albedo, Cooling degree-day, Microclimatology,Sustainable building

I. I NTRODUCTION

Using the climatic conditions of the site locality might beavoiding electro-mechanical devices and the starting point of

architectural and house technical design.

The climatic Data information is great interest insustainable building with respect to its renewable energy

potential and in obtaining an idea of the local climate.Sustainable practices in building design and operation are

becoming more and more important in the world [1]. Eventhough it varies in detail from day to day, it is neverthelessuniformly composed of three contributing influences, solar heating - wind - moisture mixed to varying degrees.

One of the most important factors affecting sustainabledesign of buildings is the consideration of climate changecontributing to all the dynamic and life-giving processes andchallenges to the present and future generations’characteristics.

Without better information and understanding of the local

climate, it is not possible to study and achieve optimal buildingdesign and efficient building service operation [2]

In arid fringe climate areas the design of buildings for comfort must address resisting summer heat inflow fromoutside - ejecting the heat buildup emanating from theoccupants and appliances inside the building. This approach isappropriate for comfort design for the majority of Iraq.

As a result of solar inflow variation with latitude, thesummer winds flow over the substantial land area is warm. Thewestern infiltrates cool air changes across Iraq in the generalwest to east flow of weather pattern. Recent studies show that

best results in energy saving can be achieved through passivedesign and recycling strategies. It has been estimated that

warm southern slopes will reduce annual heat consumptionabout 1.6-3.2 kWh/m

2[3].According to Yeang [4] the new

green skyscrapers and intensive building types should seek toachieve energy use of about 100 kWh/m² / year or less,compared with 230 kWh/m² / year for fully air-conditioned – and in the temperate zone heated – buildings and about 150-250 kWh/m² for air-conditioned offices.

The objectives of this study were to analyze of themicroclimatological factors and to evaluate and assess thedevelopment needs of building climatic design. Thisinformation will help people to understand the trends of localclimate and build up the resources for assessing importantissues of energy and environmental design.



International Journal of Science and Engineering Investigations, Volume 2, Issue 15, April 2013 84

www.IJSEI.com Paper ID: 21513-15ISSN: 2251-8843

II. DATA SOURCES

The climate responsive building design in the Iraq contextis the synthesis of theoretical hypothesis - backed by empiricalevidence - applied to building designs both in concept and reallife applications. The hypotheses will be developed from basic

meteorology and physics theory.

The general weather patterns in Iraq are typified by coolwinters with southwest winds and moisture, and hot summerswith northerly winds, either dry and dusty, or tropical in thesouth. The climate is characterized as temperate', withtemperatures outside the normal human comfort range (above45C) principally in the summer. This is an arid fringe climate.

The collection of the data for this study was governed bythe availability of free data from the Central Iraqi Weather Bureau, Baghdad Station. Due to the nature and scope of thestudy, it was realized that the analysis could only be carried outin a single geographical region in Iraq. This region is loosely

referred to Baghdad although the sources of data are fromdifferent locations within this region.

The study identified basic calculations, which rely onclimatic data for their calculation includes total energy, heatingcoefficient, net solar radiation, and albedo .

The climatic data collected for the study includes degree-day data for a Baghdad annual average of monthly mean air temperature, global solar radiation, net solar radiation, winddirection, wind speed, relative humidity, evaporation, soiltemperature.

Hourly data files for building energy analysis andsimulation actual sunshine hours and luminance parameters, as

well as statistical summaries and seasonal variations are often provided to indicate the key climate concept. The initialanalysis of the collected data involved identifying andquantifying trends over the four decades. The collecteddegree-day data to a base temperature of 26.6 °C in Baghdadwere collected for the last 50 years.

III. CLIMATIC DATA ANALYSIS

Figure 1 shows the collected mean monthly temperaturedata together with similar moving average and linear trendlines. The results of the analysis show that the annual averageof mean temperatures measured at Baghdad over the last 50

years have increased of 7%. During the last 50 years, monthlydegree-day value has decreased by some 9%.

Fig. 1. annual average of monthly cooling degree days of Baghdad, 1960 to

2010.

From the yearly cooling and heating degree-days over the50 year period (calculated for a reference temperature of 26.6°C). It can be seen that the city is warmed up as indicated bythe increasing cooling degree-days and decreasing heatingdegree days. This has significant implications to urban climateand energy use.

TABLE I. MONTHLY AVERAGE OF MEAN DAILY VALUES OF ALBEDO WERE

CALCULATED FOR EACH MONTH OF THE R ECORDED PERIOD

The degree-day method is commonly used to estimateenergy consumption in the early stages of thermal design [5] ).

To evaluate the long-term variation of degree-day temperaturesin Baghdad, a comprehensive set of degree-day figures have been established (Fig. 2).

Winter months, albedo rise quite significantly during thesummer months.

However, a large portion of the rise in albedo value at lowsolar altitude is undoubtedly a real effect of the surfacesthemselves. Most of the monthly change could due to thechange of solar altitude angle from month to month. Some of these changes may be due to the material itself.

Figure 3: Theoretical changes in air temperature for a rangeof albedo conditions at 1200hrs on the third day of a spell of

Jan Feb March April May June

0.37 0.33 0.30 0.28 0.25 0.20

July Aus Sept Oct Nov Dec

0.19 0.18 0.16 0.19 0.27 0.32





fine weather. High values of albedo mean that much of theincoming energy from the sun is reflected back into theatmosphere. This means that low albedo or non-reflectivesurfaces, absorb large amounts of energy from the sun. Theenergy is usually held or stored in the upper layers of the

absorbing material and later released once air temperatures become less than the surface of the absorbing material (oftenafter sunset). Albedo also has a significant impact on air temperature with high air temperatures associated with dark low albedo surfaces such as tarmac.

Fig. 2. Annual average of monthly heating degree days of baghdad, 1960 to

2010.

Adaptation of buildings and cities for climate change, it isnecessary to construct design weather data for future climates[6]. The selection of extreme and near-extreme data based onrisk assessment is suggested by [7] and a rational approachconsidering system reliability is proposed by [8]. In order toevaluate the risk level and allow for climate change, inherent

properties and limitations of the weather data must be analyzedand understood [9]. In some situations, long-term weather datawill be required for assessing energy performance of a specificyear or over a long-term period [10]. For example, multi-year

building energy simulation may be used for measurement andverification in energy saving performance contracts.Microclimatological data are significantly needed for assessingthe energy input [10]. Using the right typical weather year isalso important for meeting different needs and variousapplications such as renewable energy systems.

IV. ALBEDO

It is well known fact that part of the shortwave radiationreaching earth’s surface is reflected. The fraction of radiationreflected by the surface depends on the nature of the surface aswell as on the density of the materials. The monthly average of mean daily values of albedo was calculated based onmeasurements for each month of the recorded period are listedin Table 1. This table shows there is noticeable diurnal

variation in each month. Whereby for low solar elevations(solar altitude less than 30

o) and during

Fig.3. Relationships between air temperature and albedo at baghdad site.

V. NIGHT TIME NET RADIATION

The night – time net radiation represents a significant portion

of the day-time net radiation, which indicates that the most of the energy gained during the day time is lost again during the

night. The maximum negative net radiation occurred

immediately after sunset and decreased gradually, with the

usual decrease of surface temperature during the night,

reaching its minimum at sunset. The ground and buildingconditions were the main factors affecting long-wave net

radiation. The annual average of mean monthly night-time net

long wave radiation were listed in table 2.

The fact that the values of net long wave radiation at night

only varied between, -0.36 and – 1.71 MJ/m2

indicates that

there is a little monthly variation in the value of nocturnal net

radiation. Thus, the effective outgoing radiation, which forms

the only component of net radiation at night, remains fairly

constant throughout the period.

TABLE II. A NNUAL AVERAGE OF MEAN MONTHLY NIGHT-TIME NET LONG

WAVE RADIATION.


-0.36 -0.55 -0.74 -1.11 -1.19 -1.49


-1.71 -1.33 -1.01 -0.97 -0.71 -0.59





IV. HEATING COEFFICIENT

The heating coefficient is defined as the rate of change inlong wave radiation loss for a unit change in net radiation. Theheating coefficient (β) was calculated from the slope of theregression line of run plotted against Rs.

A good linear regression equation is deducted for eachannual average monthly good correlation confidants (R2 = 0.55

– 0.97).

The values of (β) [β = (1-slope) / slope] obtained for eachmonth summarized in Table 3. There is some indication fromthe data in this table that there are considerable differences inthe values of the heating coefficient for each month. Whatever the explanation, it seems that the heating coefficient should not

be considerable a characteristic exclusively of the surface, butrather as representing between properties of the buildingsurface and the atmosphere [11].

TABLE III. MONTHLY AVERAGE OF MEAN DAILY VALUES OF HEATING

COEFFICIENTS EACH MONTH OF THE RECORDED PERIOD.

V.

CONCLUSIONSThis study shows the beneficial effects of long term

microclimatological data is significantly needed for sustainable building design assessing energy input. It has been shown thatinformation will determine the effectiveness of building designstrategies.

Significant changes have taken place in Baghdad regionduring the last 50 years. Annual cooling degree-days have

reduced by 500 in 50 years (16%). Annual heating degree dayshave reduced by 360 in 50 years (26%).

Mean annual temperatures have increased 7% in 50 years.Annual solar radiation has increased by 3 W/m

2in 50 years

(3.3%).

The use of historical climatic data significantlyoverestimates building energy requirements:

Climatic data used for building design calculations should be regularly reviewed and updated, otherwise its use may resultin buildings not suitable for this region environment.

REFERENCES

[1] Langston, G. K Ding, Sustainable Practices in the Built Environment,Butterworth-Heinemann, Oxford. eds., (2001).

[2] Kivistö, R. Kari, A. KaavoitusRaportti Ija Raportti 2: Aluekohtaisettulokset ja johtopäätökset, YM Kaavoitus- ja rakennusosasto, (1987)123-124.

[3] Yeang, The green scraper, Landshut (1999) 260-266.

[4] Yang, L . Lu, Study of typical meteorological years and their effect on building energy and renewable energy simulations, ASHRAE Transactions, 110 (2) ( 2004) 424-431.

[5] Lam, Degree-day climate parameters for Hong Kong, InternationalJournal of Ambient Energy, 16 (1995) 209 – 18

[6] Belcher, J. N. and Powell, D. S.,. Constructing design weather data for future climates, Building Services Engineering Research and Technology, 26 (2005) 49-61.

[7] Chow, et al.,. Extreme and near-extreme climate change data in relationto building and plant design, Building Services Engineering Researchand Technology, 23 (4) (2002) 233-242

[8] Chen, F Yik,. and J Burnett,., A rational method for selection of

coincident design dryan wet-bulb temperatures for required systemreliability, Energy and Buildings, 37(6)(2005)555 .

[9] H. Yang, L . Lu, Study of typical meteorological years and their effecton building energ and renewable energy simulations, ASHRAE Transactions, 110 (2)( 2004) 424-431.

[10] Hui, K. P. Cheung, ,. Multi-year (MY) building simulation: is it usefuland practical?, In Proc. of the IBPSA Building Simulation '97Conference, (1997b) 8-10 Sept, 1997.

[11] Stanhill, G. Hpfstede, J.D. Kalma, Radiation balanceof naturalconditions. Q.J. R.Meteorological Soc.(92 )(1966) 128-140.


0.1 0.22 0.28 0.39 0.41 0.45


0.46 0.43 0.38 0.33 0.25 0.12

potential effects of microclimatic factors in environmental design of building in iraq context

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